The antigenic composition of Mycoplasma pneumoniae will be determined with particular emphasis on membrane protein antigens of the organism. Studies on carbohydrate and glycolipid antigens will be focused on determination of structures, composition and a particular search will be made for naturally occurring cross-reacting substances. Antigens will be purified and human sera will be tested for presence of antibody to determine which antigenic components are immunogenic during human infection. Emphasis will be placed to determining similarities and differences in strains of M. pneumoniae, particularly those strains recovered from individuals with multiple infections. Additionally the location of important antigens will be studied in terms of membrane, cytoplasmic and surface location.